1. Field of the Invention
This invention relates to guided missiles and, more particularly, it relates to a system for making corrections to guidance signals.
Over an extended flight, gravity causes the missile to droop a distance uncorrected for by the guidance. A gravity bias system corrects this error.
2. Description of the Prior Art
Missiles using pursuit guidance navigation such as the Shrike can miss the target through the combined effects of gravity, seeker boresight error, cross winds, and multi-paths. When the missile approaches the target at a shallow angle, the effect of gravity causes the missile to fall short. Missiles such as the Shrike not having a vertical reference cannot correct for the influence of gravity.
For example, the Shrike missile""s flight control is not initiated for a fixed period after launch and pressure rate of change has met a defined logic. Using the present logic, flight control is at times initiated too late in the flight for certain launch conditions and as a result the missile does not have enough guidance controlled flight time to steer to the target.
A further problem is a device for measuring air pressure. A wire wound potentiometer pressure transducer has been used in the past. Although its output is linear with pressure to a degree, its output is stepped because of the coarse windings and has a minimum resolution of xc2x110 pounds per square foot (P.S.F.). Since the output is not truly linear, differention is difficult to perform.
Another problem of past air pressure devices has been its location upon the body of the missile. If it is located near the wings, the pressure varies greatly at lower speeds.
The present invention relates to a device for initiating flight control and a device which upon said initiation corrects guidance error signals compensating for gravity bias.
After the launch of the missile, flight control is inhibited until a defined set of parameters are satisfied. Once initiated, gravity bias is a constant 2.5xc2x0 for the first 20 seconds, then gravity bias is a linear function of pressure rate.
The gravity bias circuit uses a pressure transducer having a continuous functional output with respect to the pressure rate. The pressure is differentiated and input into a gravity bias generator. The gravity bias generator outputs a bias signal which is multiplied by the outputs of a 2 degree of freedom gyro used to measure roll angle. The outputs of the gyro are a product of the bias signal and cosine or sine of the roll angle. These outputs are added or subtracted from error signals from the guidance computer. These corrected error signals are input into servos for controlling the missile flight.
One object of this invention is a variable gravity bias device whose output is a continuous function of the pressure rate.
Another object of this invention is a flight control initiating device using selective logic so that the gravity bias device can effectively control the missile.
Another object of this invention is a gravity bias device that uses a plastic potentiometer element in the pressure transducer to give a continuous output.
A further object is a variable gravity bias control system that significantly increases the missile kill probability especially for shallow approaches to the target.
A still further object is a gravity bias control system that increases the envelope in which the missile can be operated.
Other objects, advantages, and novel features of the invention shall become apparent from the following detailed description when considered in conjunction with the drawings and the claims.